Miscellaneous Problem on Limits 2

Calculus Level 3

Let f : R R f:R\rightarrow R be a positive increasing function with lim x f ( 3 x ) f ( x ) = 1 \lim _{ x\rightarrow \infty }{ \frac { f(3x) }{ f(x) } }=1 . Then lim x f ( 2 x ) f ( x ) = \lim _{ x\rightarrow \infty }{ \frac { f(2x) }{ f(x) } } =


The answer is 1.

This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try refreshing the page, (b) enabling javascript if it is disabled on your browser and, finally, (c) loading the non-javascript version of this page . We're sorry about the hassle.

1 solution

Tom Engelsman
May 30, 2020

Let f ( x ) = ln ( x ) f(x) = \ln(x) as an example. This gives lim x ln ( 3 x ) ln ( x ) = lim x ln ( 3 ) + ln ( x ) ln ( x ) = lim x ln ( 3 ) ln ( x ) + 1 = 1. \lim_{x \rightarrow \infty} \frac{\ln(3x)}{\ln(x)} = \lim_{x \rightarrow \infty} \frac{\ln(3) + \ln(x)}{\ln(x)} = \lim_{x \rightarrow \infty} \frac{\ln(3)}{\ln(x)} + 1 = 1. By the same approach:

lim x ln ( 2 x ) ln ( x ) = lim x ln ( 2 ) ln ( x ) + 1 = 1 . \lim_{x \rightarrow \infty} \frac{\ln(2x)}{\ln(x)} = \lim_{x \rightarrow \infty} \frac{\ln(2)}{\ln(x)} + 1 = \boxed{1}.

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...